Working pressure rating for cast iron (C.I.) water mains Identify the typical maximum working pressure (approximate) to which C.I. pipes may be subjected in traditional practice.
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A3 kg/cm^2
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B5 kg/cm^2
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C7 kg/cm^2
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D10 kg/cm^2
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E12 kg/cm^2
Answer
Correct Answer: 7 kg/cm^2
Explanation
Introduction / Context:Pipe classes are chosen to withstand internal pressure plus surge allowances. Traditional cast iron mains have long been rated by nominal internal pressure capability tied to wall thickness/class.
Given Data / Assumptions:
- Typical historical classes for C.I. water mains in municipal distribution.
- Working (steady) pressure, not transient surge.
Concept / Approach:Widely cited values for C.I. mains place the upper range of routine working pressures around 7 kg/cm^2 (approximately 0.7 MPa), with selection depending on diameter, class, and safety margins for transients.
Step-by-Step Solution:
Relate pressure class to practical municipal ranges (3–7 kg/cm^2 are common).Identify the upper typical working pressure for many C.I. networks: about 7 kg/cm^2.Verification / Alternative check:Historical specifications and catalogs list similar limits for standard C.I. classes; ductile iron extends capability beyond these values as needed.
Why Other Options Are Wrong:
- 3 or 5 kg/cm^2 may be too conservative for many trunk mains.
- 10 or 12 kg/cm^2 exceed typical C.I. classes used widely without special design.
Common Pitfalls:Not accounting for surge; even at 7 kg/cm^2 steady pressure, surge control (air valves, surge tanks) is vital.
Final Answer:7 kg/cm^2